1. Technical Field
The present invention relates to a positioning signal reception device and a control method of the positioning signal reception device.
2. Related Art
A GPS (Global Positioning System) device has been used as a positioning system that determines a position using an artificial satellite.
A positioning signal transmitted from a GPS satellite is a radio frequency signal modulated by the CDMA (Code Division Multiple Access) scheme. After it is received by a receiver, it is demodulated and decoded by processes, such as frequency conversion, A/D conversion, frequency separation by a filter, and synchronization of PN (Pseudo Noise) codes, so that a navigation message is obtained.
Various proposals have been made for the characteristic of the filter that performs frequency separation, because it has influences on the performance as the receiver, for example, a time needed for synchronization of PN codes and the positioning accuracy.
JP-A-5-157826 (see FIG. 9) discloses a configuration to shorten the synchronization time before the synchronization of PN codes is established by broadening the bandwidth of the filter, and to enhance the stability of synchronization after the synchronization is established by narrowing the bandwidth.
Recently, the GPS receiver is incorporated into a general-purpose small terminal, such as a cellular phone, as one of its functions. Positioning is therefore performed in a place where the radio wave reception environment is poor, such as an indoor place, more often than in a case where it is incorporated into a traditional, single-purpose positioning machine. In addition, the GPS receiver is exposed to adverse effects from the other components forming the terminal that incorporates the GPS receiver, for example, noises from the CPU (Central Processing Unit) as the source of release, interference by radio waves transmitted from a cellular phone unit, etc. more frequently than before.
The configuration in the related art, however, is not able to set an appropriate filter characteristic in response to the external environment of the GPS receiver as described above, because the characteristic of the filter is changed in response to the operating state of the GPS receiver alone. This raises a problem that the positioning takes a longer time or the positioning accuracy becomes poor depending on the external environment.